Thousands of HM Revenue and Customs staff are staging a 24-hour strike over planned job cuts.
About 8,000 staff members are expected to take part in the strike
Members of the Public and Commercial Services Union at 10 centres which deal with tax claims are taking part.
About 8,000 workers are striking after it emerged that more than 12,000 jobs may be cut. Plans to change working practices have also caused anger.
HM Revenue and Customs said it was "disappointed" by the decision to strike, calling it "unnecessary".
The offices involved in the industrial action are in Glasgow, Newcastle, Salford, Sefton (Liverpool), Wrexham, Cardiff, Portsmouth, Leicester, Bradford and Edinburgh.
The industrial action will not affect people making telephone enquiries regarding tax.
After the strike the protest will continue with an overtime ban.
'Unnecessary and unwarranted'
Earlier this month the union postponed a strike after reaching an interim agreement but claimed management back-tracked.
Mark Serwotka, PCS general secretary, said "dedicated staff" face their work being "de-skilled" and being "reduced to nothing more than robots".
"Rather than introducing outmoded working practices designed by consultants for the car industry in the 1970s, senior management need to get back around the negotiating table and start acting like a responsible employer," he said.
Meanwhile, a Revenue and Customs spokesman said: "We regard this action as unnecessary and unwarranted and will do all we can to minimise disruption."